The invention relates broadly to digital inkjet printers and in particular to digital ink jet printers configured to print the entire width of a page simultaneously.
Various methods, systems and apparatus relating to the present invention are disclosed in the following co-pending applications filed by the applicant or assignee of the present invention on May 24, 2000:
The disclosures of these co-pending applications are incorporated herein by cross-reference. Also incorporated by cross-reference, is the disclosure of a co-filed PCT application, PCT/AU01/00217 (deriving priority from Australian Provisional Patent Application No. PQ5957).
Traditionally, inkjet printers have used a printing head that traverses back and forth across the width of a page as it prints. Recently, it has been possible to form printheads that extend the entire width of the page so that the printhead can remain stationary as the page is moved past it. As pagewidth printheads do not move back and forth across the page, much higher printing speeds are possible.
Pagewidth printheads are typically micro electro mechanical systems (MEMS) devices that are manufactured in a manner similar to silicon computer chips. In this process, the ink nozzles and ejector mechanisms are formed in a series of etching and deposition procedures on silicon wafers.
As an industry standard, the silicon wafers are produced in 6 or 8 inch diameter disks. Consequently only a small strip across the diameter of each wafer can be used to produce printing chips of sufficient width for pagewidth printing. As a large part of these wafers are essentially wasted, the production costs of pagewidth printhead chips are relatively high.
The costs are further increased because the chip defect rate is also relatively high. Faults will inevitably occur during silicon chip manufacture and some level of attrition is always present. A single fault will render an entire pagewidth chip defective, as is the case with any silicon chip production. However, because the pagewidth chip is larger than regular chips, there is a higher probability that any particular pagewidth chip will be defective thereby raising the defect rate as a whole in comparison to regular silicon chip production.
To address this, the pagewidth printhead may be formed from a series of separate printhead modules. Using a number of adjacent printhead modules permits full pagewidth printing while allowing a much higher utilization of the silicon wafer. This lowers the printhead chip defect rate because a fault will cause a relatively smaller printhead chip to be rejected rather than a full pagewidth chip. This in turn translates to lower production costs.
Each printhead chip carries an array of nozzles which have mechanical structures with sub-micron thickness. The nozzle assemblies use thermal bend actuators that can rapidly eject ink droplets sized in the Pico liter (xc3x9710xe2x88x9212 liter) range.
The microscopic scale of these structures causes problems when butting a series of printhead modules end to end in order to form a pagewidth printhead. Microscopic irregularities on the end surfaces of each chip prevent them from perfectly abutting the end surface on an adjacent chip. This causes the spacing between the end nozzles of two adjacent printhead chips to be different from adjacent nozzles on a single printhead chip. The gaps between adjacent printhead chips can lower the resultant print quality.
To eliminate the gaps, some modular pagewidth printheads use two adjacent lines of regularly spaced printhead modules. The lines are out of register with each other and the ends of a printhead module in one line overlaps with the ends of two adjacent modules in the other line. This removes the gaps from the resultant printing but also provides redundant nozzles in the areas of overlap. The print data to the overlapping nozzles is allocated between the adjacent chips so that these areas are not printed twice which would otherwise have adverse affects on the print quality.
A digital controller is connected to each of the printhead module chips via a TAB (tape automated bond) film. The TAB film is substantially the same width as the chip and this causes difficulties when mounting the chips to a support structure within the printer. It is preferable that the TAB films for each chip extend from the same side as this permits a more compact and elegant printhead design. However, this arrangement requires the TAB films from each of the chips in one of the lines to narrow or xe2x80x98neckxe2x80x99 in order to fit past the restriction caused by the overlapping ends of the adjacent chips in the other line. Producing and installing TAB films that narrow down enough is complex and difficult. To avoid this, the TAB films can extend from one side of the chips in one line and from the opposite side of the chips in the other line. However, as discussed above this gives the overall printhead greater bulk that can complicate the paper path through the printer as well as hamper capping the printheads when the printer is not in use.
Accordingly, the present invention provides a modular printhead for a inkjet printer, the modular printhead including:
a support frame;
a plurality of printhead modules mounted to the support frame, each module having an elongate array of ink nozzles extending substantially linearly across the width of the module such that there is overlap between the elongate arrays of adjacent modules with respect to the direction of paper movement; wherein,
the modules are arranged such that a first side of each of the nozzle arrays faces toward a first side of the support frame; such that,
the respective first sides of predominantly all of the nozzle arrays have at most one end portion obscured from the first side of the support frame by the nozzle array of an adjacent module.
Preferably, the respective first sides of each of the nozzle arrays have at most one end portion obscured from the first side of the support frame by the nozzle array of an adjacent module.
By inclining the printhead chips with respect to the support beam and configuring them to overlap with respect the to paper direction, the TAB films for each chip can extend from the same side. This allows the printhead design to remain relatively compact while avoiding the need to significantly narrow or xe2x80x98neckxe2x80x99 most if not all the TAB films.
Preferably, the modules are mounted to the support frame along a substantially straight mounting line such that each of the elongate arrays extends in a direction inclined to the mounting line of the modules. In a further preferred form, the mounting line is normal to the paper direction.
Preferably, the printhead is digitally controlled such that print data sent to the overlapping portions of adjacent modules is shared between the ink nozzles of the adjacent modules to avoid double printing of the same data.
In a particularly preferred form, the digital controller starts to place print data with the nozzles in an adjacent module at the one edge of the overlapping portion, and ramps up the data directed to the nozzles of the adjacent module stochastically until all the print data is directed to the adjacent module at the opposing edge of the overlapping portion.
Preferably, the printhead is a pagewidth printhead.
In a further preferred form, the printhead modules are adapted to be individually removed and replaced. To achieve this the printhead modules may be conveniently adapted for snap-locking engagement with the support frame.
It will be appreciated that the adjacent positioning of a number of small modular printheads permits full pagewidth printing while allowing a much higher utilization of the silicon wafer. Furthermore, the defect rate is effectively lower because a single fault will mean that a relatively smaller printhead chip will be rejected rather than a large full pagewidth printhead chip. Accordingly, the production costs per chip are significantly reduced.
By providing each modular printhead with snap-lock formations, it is convenient to individually remove and replace defective modules.